Lightweight and rigid structure of battery unit

ABSTRACT

A battery unit is provided which includes a battery and a storage case in which the battery is mounted. The storage case is made up of a base, a cover, and an intermediate case. The cover is jointed to the base with an interspace therebetween. The intermediate case is disposed between the cover and the base and has a peripheral wall which occupies the interspace. The intermediate case is lower in stiffness than the cover and the base, thereby realizing a lightweight structure of the storage case without sacrificing the mechanical strength thereof.

CROSS REFERENCE TO RELATED DOCUMENT

The present application claims the benefit of priority of Japanese Patent Application No. 2013-36764 filed on Feb. 27, 2013, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates generally to a battery unit which includes a storage battery disposed in a storage case mounted in vehicles such as automobiles.

2. Background Art

Battery units are known which include a storage battery (also called an assembled battery module) equipped with a plurality of electrochemical cells and disposed in a storage case in the form of a battery pack mounted in vehicles such as automobiles. This type of battery units are concerned about being stepped by people at places of installation thereof and thus shaped to improve the mechanical strength thereof. For instance, in the case where the battery unit is mounted in an automotive vehicle, it may be located in a passenger compartment because it is desirable to place the battery unit away from hot environments in terms of characteristics thereof. It is, however, concerned that the battery unit is stepped in error by occupants in the passenger compartment or the occupants mistakenly drop things on the battery unit, thus requiring the battery unit to have a mechanical strength great enough to withstand the external force.

For instance, Japanese Patent First Publication No. 2006-339031 teaches a battery pack which includes a storage battery equipped with a stack of electrochemical cells each covered with laminate films (which will also be referred to as laminated cells or laminated-type cells below). The battery pack also includes a storage case, a cover, and clampers. The storage case has the storage battery installed therein. The storage case has an open end closed by the cover. The cover is pressed by the clamper to hold the storage battery under pressure within the storage case. The storage case is made of metal such as aluminum material which is shaped to have a thickness achieving a desired mechanical strength.

Generally, the stiffness or rigidity of the whole of the storage case is enhanced in order to increase the mechanical strength against the external force. This, however, results in an increased in weight of the battery unit, which is inconvenient for installation thereof in the automotive vehicles.

SUMMARY OF THE INVENTION

It is therefore an object of this disclosure to provide a lightweight structure of a battery unit which is equipped with a storage case designed to have a mechanical strength great enough to withstand external force.

According to one aspect of the embodiment, there is provided a battery unit which may be employed with automatic vehicles. The battery unit comprises: (a) a battery; and (b) a storage case in which the battery is installed. The storage case includes a first casing member, a second casing member, and an intermediate casing member. The first casing member defines a bottom of the storage case. The second casing member defines a top of the storage case with the battery disposed between itself and the first casing member. The second casing member is joined to the first casing member so as to create a clearance which extends along a circumference of a peripheral wall of the storage case. The intermediate casing member is disposed between the first casing member and the second casing member to form an intermediate wall that is a portion of the peripheral wall of the storage case. The intermediate casing member is lower in stiffness than the first and second casing members.

When only the second casing member is secured to the first casing member, a square space (i.e., a clearance) is created between the second casing member and the first casing member, that is, in the peripheral wall of the storage case. The square space extends along the entire circumference of the peripheral wall of the storage case. The intermediate casing member is used to occupy the square space to form a portion of the peripheral wall of the storage case. The use of the intermediate casing member results in omission of a portion of the wall of either of the first casing member or the second casing member which corresponds to the profile of the square space. The first casing member is attached to the second casing member, thereby ensuring a desired degree of mechanical strength of the first casing member and the second casing member regardless of the intermediate casing member. Specifically, the intermediate casing member is lower in stiffness than the first casing member and the second casing member, however, the attachment of the second casing member to the first casing member ensures a required degree of mechanical strength of the storage case independently of the intermediate casing member.

Consequently, when undesirable load arising from, for example, stepping on of the storage case, is exerted between the first casing member (i.e., the bottom of the storage case) and the second casing member (i.e., the top of the storage case), a combination of the first casing member and the second casing member bears the whole of the storage case against the load to protect the battery unit from the external force.

The attachment of the second casing member to the first casing member permits the intermediate casing member, as described above, to be lower in stiffness than the first casing member and the second casing member, thus allowing the intermediate casing member to be made of a lightweight material or designed to have a lightweight structure. For instance, the first casing member and the second casing member may be each made from metal such as aluminum, while the intermediate casing member may be made of synthetic resin. This results in a decreased overall weight of the storage case, thus permitting the battery unit to be lightweight, yet have mechanical strength great enough to withstand possible external forces.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detailed description given hereinbelow and from the accompanying drawings of the preferred embodiments of the invention, which, however, should not be taken to limit the invention to the specific embodiments but are for the purpose of explanation and understanding only.

In the drawings:

FIG. 1 is a perspective view which shows an overall structure of a battery unit according to an embodiment;

FIG. 2 is a transverse sectional view, as taken long the line II-II in FIG. 1;

FIG. 3 is an exploded perspective view which shows essential parts of the battery unit of FIG. 1;

FIG. 4 is a perspective view which illustrates a base on which an assembled battery module is mounted;

FIG. 5 is a plane view of FIG. 4;

FIG. 6 is a bottom view which illustrates a cover fastened to the base of FIG. 5;

FIG. 7 is a perspective view which illustrates an intermediate case disposed between the base of FIG. 4 and the cover of FIG. 6;

FIG. 8(a) is a plane view of the intermediate case of FIG. 7;

FIG. 8(b) is a bottom view of the intermediate case of FIG. 7;

FIG. 9 is a vertical sectional view, as taken along the line IX-IX in FIG. 8(a);

FIG. 10 is an enlarged perspective view of a water damage sensor;

FIG. 11 is a vertical section view of a base and an intermediate case of a storage case which illustrates a vertical location of the water damage sensor of FIG. 10;

FIG. 12 is a perspective view which shows an assembled battery module mounted in the battery unit of FIG. 1;

FIG. 13 is an exploded perspective view which illustrates an assembled battery module;

FIG. 14 is an exploded perspective view which illustrates an assembled battery module;

FIG. 15 is a side view which illustrates joints of electrode tabs of cells of an assembled battery module;

FIG. 16 is a plane view which illustrates an assembled battery module mounted on a base of a storage case of the battery unit of FIG. 1;

FIG. 17 is a perspective view which illustrates a control board installed in the battery unit of FIG. 1;

FIG. 18 is a plane view which illustrates the control board of FIG. 17 mounted on a base of a storage case; and

FIG. 19 is a circuit diagraph which shows an electric structure of a power supply system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, wherein like reference numbers refer to like parts in several views, particularly to FIGS. 1 to 3, there is shown a battery unit 10 which is used, as an example, with a power supply system installed in an automotive vehicle equipped with an internal combustion engine, an electronic control unit (ECU) working to control operations of the engine or other electric devices, an electric generator (also called an alternator) which is driven by the engine to generate electricity, and an electric storage device which is charged by electric power produced by the generator. The electric storage device includes a lead acid battery and lithium-ion battery. The battery unit 10, as will be described below, is designed as the lithium-ion battery.

The overall structure of the battery unit 10 will be described below with reference to FIGS. 1 to 3. A vertical direction of the battery unit 10, as referred to in the following discussion, is based on orientation of the battery unit 10 placed, as illustrated in FIG. 1, on a horizontal plane for the sake of convenience.

The battery unit 10 consists essentially of an assembled battery module 11, a control board 12, and a storage case 13. The assembled battery module 11 is made up of a stack of laminated-type cells each covered with a laminate film. The control board 12 works as a controller to control charging or discharging of the assembled battery module 11. The storage case 13 has the assembled battery module 11 and the control board 12 installed therein and is made up of a base 14 (which will also be referred to as a first casing member), a cover 15 (which will also be referred to as a second casing member), and an intermediate case 16 (which will also be referred to as an intermediate casing member). The base 14 is fixed at a place where the battery unit 10 is installed. The cover 15 is arranged above the base 14. The intermediate case 16 is joined intermediate between the base 14 and the cover 15 as a side shell defining a portion of a side or peripheral wall of the storage case 13. The assembled battery module 11 and the control board 12 are laid to overlap each other vertically. Specifically, the control board 12 is disposed above the assembled battery module 11. The assembled battery module 11 and the control board 12 are fixed to the base 14. The cover 15 and the intermediate case 16 are also fastened to the base 14.

The battery unit 10 is equipped with a terminal block 17 for electric connection with an external lead-acid battery or an electric generator and an electric connector 18 for electric connection with the ECU mounted in the vehicle. The electric connector 18 is also joinable to other electric loads to which the power is to be supplied from the battery unit 10. The terminal block 17 and the connector 18 are, as can be seen in FIG. 1, partially exposed outside the battery unit 10.

The structure of the battery unit 10 will be described below in detail.

Base 14 of Storage Case 13

The base 14 of the battery unit 10 will be explained. FIG. 4 is a perspective view of the base 14. FIG. 5 is a plane view of the base 14.

The base 14 is made from a metallic material such as aluminum and includes a bottom plate 21 and an upright wall 22 extending vertically from the bottom plate 21. The bottom plate 21 is substantially square in shape and has a circumferential edge from which the upright wall 22 extends. In other words, the upright wall 22 surrounds the circumference edge of the bottom plate 21. The bottom plate 21 serves as a module mount on which the assembled battery module 11 is retained. The upright wall 22 is so shaped as to completely encompass the assembled battery module 11 mounted on the bottom plate 21.

The base 14, as illustrated in FIG. 5, has a module mount surface 23 which is defined by a portion of a bottom wall of the base 14 and with which the assembled battery module 11 is mounted in direct contact. The module mount surface 23 protrudes slightly from its surrounding area of the base 14 and has an upper even surface formed by, for example, grinding or polishing. The upright wall 22 is of an annular shape and surrounds the assembled battery module 11.

To the base 14, the assembled battery module 11, the control board 12, the cover 15, and the intermediate case 16 are fastened. Specifically, the base 14 has a plurality of cylindrical fixing portions 24 a to 24 d which are used as fastener supports for securing the assembled battery module 11, the control board 12, the cover 15, and the intermediate case 16 to the base 14. The cylindrical fixing portions 24 a to 24 d will be also generally denoted by a reference number 24 below. The cylindrical fixing portions 24 a are the fastener supports for the control board 12. The cylindrical fixing portions 24 b are the fastener supports for the cover 15. The cylindrical fixing portions 24 a and 24 b extend vertically from the bottom of the base 14 inside the upright wall 22 and have top ends on which the control board 12 and the cover 15 are mounted. The base 14 also has formed on inner corners of the upright wall 22 base blocks 25 on which some of the cylindrical fixing portions 24 a and 24 b extend upwardly.

The cylindrical fixing portions 24 c are the fastener supports for the assembled battery module 11 and located inside the upright wall 22. The cylindrical fixing portions 24 c are lower in height than the upper end of the upright wall 22. The cylindrical fixing portions 24 d are the fastener supports for the intermediate case 16 and located outside the upright wall 22.

The top end of each of the cylindrical fixing portions 24 a to 24 d has an even surface extending in the same direction as that in which the bottom surface of the bottom plate 21 extends. The top end of each of the cylindrical fixing portions 24 a to 24 b has a threaded hole formed therein. The installation of the assembled battery module 11, the control board 12, the cover 15, and the intermediate case 16 on the base 14 is achieved by placing them on the top ends of the cylindrical fixing portions 24 a to 24 d and then fastening screws N into the threaded holes of the cylindrical fixing portions 24 a to 24 d. The cylindrical fixing portions 24 a to 24 may be formed in another shape and located either inside or outside the upright wall 22.

The base 14 also has a plurality of cylindrical locating pins 26 (two in this embodiment) extending upwardly, like the cylindrical fixing portions 24 a and 24 b. Each of the locating pins 26 has an outer shoulder and is made up of a small-diameter portion and a large-diameter portion. The small-diameter portion works as a positioner to position the control board 12 relative to the base 14.

The base 14 is equipped with a heat dissipator which serves to release heat, as generated by the assembled battery module 11 and the control board 12, to the environment. Specifically, the base 14 has, as illustrated in FIGS. 4 and 5, a heat sink 27 formed as the heat dissipator on the base plate 21 inside the upright wall 22. The heat sink 27 includes a board-facing plate 27 a facing the back surface of the control board 12 and a plurality of fins (not shown) disposed below the board-facing plate 27 a. The heat sink 27 is opposed to an area of the control board 12 in which power devices P are mounted. The heat, as produced by the power devices P, is transmitted to the board-facing plate 27 a and then released from the fins outside the battery unit 10.

The power devices P are implemented by power semiconductor devices. Specifically, power transistors such as power MOSFETs or IGBTs are mounted as the power devices P on a power path leading to the assembled battery module 11 in the battery unit 10. The power devices P are turned on or off to control input or output of electric power into or from the assembled battery module 11. The battery unit 10 is, as described above, connected to the lead-acid battery and the electric generator. The power path leading to the assembled battery module 11 is, thus, connected to the lead-acid battery and the electric generator.

The base 14 has formed on the lower surface of the base plate 21 ribs (not shown) as a heat dissipator. The heat, as produced by the assembled battery module 11, is transmitted to the module mount surface 23 of the bottom plate 21 and then released from the ribs outside the battery unit 10. Similarly, the heat, as produced by the control board 12, is transmitted from the heat sink 27 to the bottom plate 21 and then released from the ribs on the bottom plate 21 outside the battery unit 10. The ribs also work as reinforcements.

The upright wall 22 also has formed therein a gas drain port 28 from which gas in the storage case 13 is drained outside the battery unit 10. The bottom plate 21 also has flanges 29 extending outwardly from the upright wall 22. Each of the flanges 29 has a hole through which a bolt passes for installation of the battery unit 10.

Cover 15

FIG. 6 is a bottom view of the cover 15. The cover 15 is, like the base 14, made from a metallic material such as aluminum. The cover 15 is substantially square in shape and identical in size in a planar view thereof with the base 14 from which the flanges 29 are omitted. The cover 15 has formed on peripheral edges or corners thereof fixing portions 31 which are used as fastener supports to mechanically connect the cover 15 to the base 14. The cover 15 also has formed therein an annular groove 32 in which an upper end of the intermediate case 16 (i.e., an upper end of an intermediate wall 41, as will be described later) is fit. The fixing portions 31 are located at the four corners of the cover 15 in alignment with the cylindrical fixing portions 24 b of the base 14. Each of the fixing portions 31 has a threaded hole formed therein. The annular groove 32 extends outside the fixing portions 31 and has a contour conformed to the contour of the upper end of the upright wall 22 of the base 14. The cover 15 has reinforcement ribs 33 formed on the lower surface thereof.

The cover 15 has formed on the lower surface thereof a spring holder 35 designed as a pressing mechanism holder. The spring holder 35 are also used as a spring press to hold coil springs 101, as disposed between the assembled battery module 11 and the cover 15, under pressure. The spring holder 35, as illustrated in FIG. 2, protrude downward from the lower surface of the cover 15 and has formed therein a plurality of cylindrical chambers 35 a in which the coil springs 101 are disposed. A pressing mechanism using the coil springs 101 will be described later in detail.

The ribs 33 are disposed in a pattern radiating from the spring holder 35 to minimize the deformation or warp of the cover 15 arising from application of a mechanical load (i.e., reactive force of the springs 101 oriented to lift the cover 15 upward) to the spring holder 35. Specifically, the spring holder 35 works as a spring support to retain one of ends of each of the coil springs 101. The ribs 33 work as a deformation avoider to minimize the deformation of the cover 15.

The attachment of the cover 15 to the base 14 is achieved by placing each of the fixing portions 31 of the cover 15 on one of the cylindrical fixing portions 24 b of the base 14 and fastening the screws N into the fixing portions 31 and the cylindrical fixing portions 24 b. The cover 15 is, as can be seen from FIG. 2, located above the upright wall 22 of the base 14, so that a generally square closed window which is unoccupied by both the cover 15 and the base 14 is formed in a peripheral wall of the storage case 13.

Intermediate Case 16

The structure of the intermediate case 16 will be described below. FIG. 7 is a perspective view of the intermediate case 16. FIG. 8(a) is a plane view of the intermediate case 16. FIG. 8(b) is a bottom view of the intermediate case 16. FIG. 9 is a sectional view, as taken along the line 9-9 in FIG. 8.

The intermediate case 16 is made of synthetic resin which is lower in stiffness than material of the base 14 and the cover 15. The intermediate case 16 is affixed to the base 14 and continuously extends from the upright wall 22 upward. The cover 15 is mounted on the intermediate case 16. The intermediate case 16 closes the above described square closed window, as unoccupied by both the cover 15 and the base 14.

The intermediate case 16, as illustrated in FIGS. 7, 8(a), and 8(b), has the intermediate wall 41 of a generally square closed shape which forms a portion of the peripheral wall of the storage case 13. The intermediate case 16 has a square closed frame 42 which defines a lower end thereof. The frame 42 has formed therein a square closed groove 43 in which the upper end of the upright wall 22 of the base 14 is fit. The frame 42 has fixing portions 44 formed outside the groove 43 fixing portions 44 which are affixed to the base 14 in the same direction as that in which the cover 15 is joined to the base 14. The fixing portions 44 are located in alignment with the fixing portions 24 d of the base 14 and have threaded holes formed therein. The threaded holes extend through the thickness of the fixing portions 44, respectively. The attachment of the intermediate case 16 to the base 14 is achieved by placing the fixing portions 44 on the fixing portions 24 d of the base 14 and then fastening screws N into the fixing portions 24 d and 44. The intermediate case 16 is disposed on the top end of the upright wall 22 of the base 14.

The intermediate wall 41 has inner tabs in which holes 45 are formed through which the locating pins 26 (i.e., the large-diameter portion) of the base 14 pass, respectively. The intermediate wall 41 is located over the upright wall 22 of the base 14 and continues to the upper end of the upright wall 22.

The intermediate case 16 has disposed integrally thereon a connecting terminal 47 which is electrically joined to a terminal block 17. The intermediate case 16 also has a connector 18 affixed thereto. The connecting terminal 47 and the connector 18 are arranged adjacent each other in or on the same one of four side walls of the intermediate case 16.

The connector 18 is partially exposed outside the intermediate case 16 and made up of a connector shell 51 into which a connector of a cable harness (not shown) is fit and a male plug 52 with a plurality of terminal pins 53 arrayed inside the connector shell 51. The terminal pins 52 partially extend upward and are electrically soldered to the control board 12. The terminal pins 53 include electric power output terminals (e.g., bus bars) and signal input/output terminals.

The intermediate case 16 is equipped with a water damage sensor 60 disposed inside the intermediate wall 41. The water damage sensor 60 is located closer to the male plug 52 and works as a submergence detection sensor to detect the ingress of water into the battery unit 10, that is, whether the battery unit 10 has been submerged in water or not. FIG. 10 is an enlarged perspective view of the water damage sensor 60.

The water damage sensor 60 essentially consists of an extension plate 61 and a sensor substrate 62. The extension plate 61 extends downward from the frame 42. The sensor substrate 62 is affixed to the extension plate 61. The extension plate 61 is square and has a plurality of connecting terminals (i.e., electric conductors) 63 which are partially embedded therein. The connecting terminals 63 are each made of a bus bar. Each of the connecting terminals 63 has an end which extends upward from an upper end of the extension plate 61 and the other end which extends horizontally from a side surface 61 a (i.e., a major surface) of the extension plate 61 on which the sensor substrate 62 is mounted. Specifically, each of the connecting terminals 62 is bent at right angles within the extension plate 61. The side surface 61 a (which will also be referred to as a substrate-mounted surface below) of the extension plate 61 has two cylindrical protrusions 64 formed on. Each of the cylindrical protrusions 64 is made up of two sections: a small-diameter portion and a large-diameter section. The cylindrical protrusions 64 are located at corners of the substrate-mounted surface 61 a of the extension plate 61.

The sensor substrate 62 has formed therein an array of holes 65 in which pins 63 a that are the lower ends of the connecting terminals 63 are fit and a pair of holes 66 into which the cylindrical protrusions 64 of the extension plate 61 are inserted. The attachment of the sensor substrate 62 to the substrate-mounted surface 61 a of the extension plate 61 is achieved by inserting the pins 63 a of the connecting terminals 63 and the cylindrical protrusions 64 of the extension plate 61 into the holes 65 and 66 and thermally staking heads of the cylindrical protrusions 64. After affixed to the extension plate 61, the sensor substrate 62 is oriented to have major surfaces extending vertically. The sensor substrate 62 has two slits 67 formed in a lower end thereof. The slits 67 extend vertically in parallel to each other. The sensor substrate 62 also has three water detecting electrodes 68 affixed adjacent the slits 67.

FIG. 11 illustrates the location of the water damage sensor 60 when the intermediate case 16 is attached to the base 14. FIG. 11 is a vertical section view of the water damage sensor 60 when the intermediate case 16 and the base 14 are assembled together.

The extension plate 61 is disposed inside the upright wall 22 of the base 14 when the intermediate case 16 is joined to the base 14. The sensor substrate 62 is located inside the extension plate 61. The three water detecting electrodes 68 are arranged lower than the lower end of the extension plate 61 (i.e., the upper end of the upright wall 22 of the base 14) and near the bottom plate 21. When the water enters the storage chamber 13, it will reach the water detecting electrodes 68 relatively quickly. This causes the water detecting electrodes 68 to be electrically connected to each other to output a signal indicative thereof to the control board 12.

The sensor substrate 62 is, as illustrated in FIG. 11, located beneath the control board 12 and has the major surface (i.e., an electronic component-mounted surface) traversing (i.e., extending substantially perpendicular to) the major surface (i.e., the electronic component-mounted surface) of the control board 12. The water detecting electrodes 68 are disposed at a level lower than an apparent boundary, as denoted by “K” in FIG. 11, between the base 14 and the intermediate case 16. The apparent boundary K lies between the top end of the upright wall 22 of the base 14 and the lower surface of a sealing member 75 fit in the groove 43 of the intermediate case 16. The control board 12 is located higher than the apparent boundary K. The direction in which the sensor substrate 62 extends is identical with that in which electrochemical cells 83 of the assembled battery module 11 are, as clearly illustrated in FIG. 2, laid to overlap each other.

The intermediate case 16, as illustrated in FIG. 7, includes insulating walls 71 extending downward from the frame 42. In the assembly of the intermediate case 16 and the base 14, the insulating walls 71, as clearly illustrated in FIG. 2, continue or extend from the intermediate case 16 toward the bottom plate 21 of the base 14 inside the upright wall 22. In other words, each of the insulating walls 71 is laid to overlap the upright wall 22 in the horizontal direction (i.e., a direction perpendicular to the thickness of the battery unit 10). The insulating walls 71 work to electrically isolate electrodes (i.e., electrode tabs 84 and 85 which will be described later in detail) of the assembled battery module 11 from the upright wall 22 and are located between the electrodes of the assembled battery module 11 and the upright wall 22. The base 14, as described above, has the base blocks 25 located inside the upright wall 22. Each of the insulating walls 71 is, as clearly illustrated in FIGS. 8(a) and 8(b), of an L-shape, in other words, has two wall sections extending perpendicular to each other to electrically isolate the electrodes of the assembled battery module 11 from the base blocks 25.

FIG. 2 illustrates the cover 15 and the intermediate case 16 which are fastened to the base 14. The upper end of the upright wall 22 of the base 14 is fit in the groove 43 of the frame 42 of the intermediate case 16. Specifically, the base 14 is fixed to the intermediate case 16 with the lower ends of the fixing portions 44 of the intermediate case 16 being in contact with the fixing portions 24 d of the base 14. In this condition, the bottom of the groove 43 of the intermediate case 16 (i.e., one of opposed ends of the intermediate wall 41 which faces the base 14) is located at a given distance away from the upper end of the upright wall 22. The sealing member 75 (i.e., a mechanical seal) fills such an air gap between the groove 43 of the intermediate case 16 and the upper end of the upright wall 22. The sealing member 75 has a configuration, as illustrated in FIG. 3. The sealing member 75 is elastically compressed by the upper end of the upright wall 22 to create a liquid and air tight seal between the base 14 and the intermediate case 16.

The upper end of the intermediate wall 41 of the intermediate case 16 is fit in the groove 43 extending along the peripheral edge of the cover 15. Specifically, the cover 15 is fixed to the base 14 with the lower ends of the fixing portions 31 of the cover 15 being in contact with the fixing portions 24 b of the base 14. In this condition, the bottom of the groove 32 of the cover 15 (i.e., one of opposed ends of the cover 15 which faces the base 14) is located at a given distance away from the upper end of the intermediate wall 41. A sealing member 76 (i.e., a mechanical seal) fills such an air gap between the groove 32 of the cover 15 and the upper end of the intermediate wall 41. The sealing member 76 has a configuration, as illustrated in FIG. 3. The sealing member 76 is elastically compressed by the upper end of the intermediate wall 41 to create a liquid and air tight seal between the cover 15 and the intermediate case 16. Instead of the sealing members 75 and 76, another type of seal such a liquid seal may be used. For instance, the liquid seal is applied to the grooves 43 and 32 and then hardened.

As apparent from the above discussion, the upper end of the upright wall 22 of the base 14 is placed in indirect contact with the bottom of the groove 43 of the intermediate case 16. Similarly, the upper end of the intermediate wall 41 of the intermediate case 16 is placed in indirect contact with the bottom of the groove 32 of the cover 15. In other words, buffers are disposed between the base 14 and the intermediate case 16 and between the intermediate case 16 and the cover 15 to avoid direction transmission of external force acting on the cover 15 from above to the intermediate case 16 and to the base 14.

Assembled Battery Module 11

The structure of the assembled battery module 11 will be described below. FIG. 12 is a perspective view which illustrates the overall structure of the assembled battery module 11. FIGS. 13 and 14 are exploded perspective views of the assembled battery module 11.

The assembled battery module 11 works as a so-called battery and consists essentially of a battery assembly 81 of a plurality of (four in this embodiment) cells 83 and a battery holder 82 fastened to the battery assembly 81. The battery assembly 81 includes the cells 83 each of which is implemented by a laminated-type cell, as described in the introductory part of this application. Specifically, each of the cells 83 is made up of a flexible flattened casing formed by a pair of laminated films and a square cell body disposed in the casing. The cells 83 are laid to overlap each other in a thickness-wise direction thereof. Each of the cells 83 is of a planar shape and has a pair of electrode tabs 84 and 85 extending outward from the cell body. The electrode tabs 84 and 85 are affixed to diametrically opposed two of four sides of each of the cells 83. The electrode tab 84 serves as a positive electrode. The electrode tab 85 serves as a negative electrode. The positive electrode tab 84 is made of aluminum. The negative electrode tab 85 is made of copper.

The cells 83 are, as described above, stacked vertically. One of vertically adjacent two of the cells 83, as can be seen from FIGS. 12 and 13, has the positive electrode tab 84 disposed on the same side as the negative electrode tab 85 of the other cell 83. In other words, the positive electrode tab 84 of one of vertically adjacent two of the cells 83 is laid over the negative electrode tab 85 of the other cell 83 in the thickness-wise direction of the cells 83. The positive electrode tab 84 of each of the cells 83 is electrically joined to the negative electrode tab 85 of an adjacent one of the cells 83, so that all the cells 83 are electrically connected together in series.

The positive electrode tab 84 and the negative electrode tab 85 of adjacent two of the cells 83 are so physically bent as to get close to each other to have portions laid to overlap each other vertically. Such overlapped portions are joined together, for example, by ultrasonic welding. In this embodiment, the positive electrode tab 84 and the negative electrode tab 85 of the battery assembly 81 are joined in the way, as illustrated in FIG. 15. Specifically, on the right side of the battery assembly 81, the uppermost positive electrode tab 84 and the lowermost negative electrode tab 85 extend straight in the horizontal direction, while the uppermost positive electrode tab 84 and the lowermost negative electrode tab 85 of intermediate two of the cells 83 are bent and welded together. On the left side of the battery assembly 81, the positive electrode tab 84 and the negative electrode tab 85 of upper two of the cells 83 are bent and welded together. Similarly, the positive electrode tab 84 and the negative electrode tab 85 of lower two of the cells 83 are bent and welded together.

An adhesion tape 86 is, as illustrated in FIG. 14, interposed between every two of the cells 83 to bond all the cells 83 together. The battery assembly 81 also has a rigid plate 87 affixed to the surface of the uppermost one of the cells 83 through the adhesion tape 86. The rigid plate 87 is made of, for example, iron sheet which has a surface area which is at least equal to that of each of the cells 83. In this embodiment, the surface area of the rigid plate 87 is greater in size than those of the cells 83. The rigid plate 87 serves as a spring support to mechanical loads, as produced by the coil springs 101.

The battery holder 82 is equipped with a first retainer 91, a second retainer 92, and a connector 93 which connects the first and second retainers 91 and 92 together. The first retainer 91 is attached to the electrode tabs 84 and 85 on one of the sides of the battery assembly 81, while the second retainer 92 is attached to the electrode tabs 84 and 85 on the opposed side of the battery assembly 81. The first retainer 91, the second retainer 92, and the connector 93 are formed integrally by synthetic resin.

Specifically, the first retainer 91 has two bus bars 94 a, 94 b, and 94 c which will be generally denoted by reference numeral 94 below. The bus bars 94 a, 94 b, and 94 c are cantilevered by the first retainer 91 and electrically connected to the positive and negative electrode tabs 84 and 85 extending from one of the opposed two of the sides of the battery assembly 81. The bus bars 94 a, 94 b, and 94 c have major surfaces facing each other in the vertical direction (i.e., the thickness-wise direction of the battery assembly 81). Each of the bus bars 94 a, 94 b, and 94 c has one of the major surfaces which is joined in contact with the surface of a corresponding one of the positive and negative electrode tabs 84 and 85, as illustrated on the right side of FIG. 15. The bus bar 94 a works as a positive terminal of the battery assembly 81 (i.e., a positive terminal of a series circuit made up of the cells 83 connected in series). The bus bar 94 c work as a negative terminal of the battery assembly 81 (i.e., a negative terminal of the series circuit). The bus bars 94 a and 94 c are connected to the power terminals 95 of the battery assembly 81, respectively.

The second retainer 92 has three bus bars 94 d and 94 e which will be generally denoted by reference numeral 94 below. The bus bars 94 d and 94 e are cantilevered by the second retainer 92 and electrically connected to the positive and negative electrode tabs 84 and 85 extending from the other of the opposed two of the sides of the battery assembly 81. The bus bars 94 d and 94 e have major surfaces facing each other in the vertical direction (i.e., the thickness-wise direction of the battery assembly 81). Each of the bus bars 94 d and 94 e has one of the major surfaces which is joined in contact with the surface of a corresponding one of the positive and negative electrode tabs 84 and 85, as illustrated on the left side of FIG. 15.

The battery assembly 81 is designed to measure a terminal voltage appearing at each of the cells 83. Specifically, the first retainer 91 has three voltage detecting terminals 96 connected to the bus bars 94 a, 94 b, and 94 c, respectively. The second retainer 92 has two voltage detecting terminals 96 connected to the bus bars 94 d and 94 e. The power terminals 95 and the voltage detecting terminals 96 all extend upward and have top ends joined to the control board 12.

Each of the voltage detecting terminals 96 may be made by a portion of one of the bus bars 94. In other words, each of the bus bars 94 may be used in detecting the terminal voltage at the cells 83. In this embodiment, each of the bus bars 94 is connected at one end to one of the positive and negative electrode tabs 84 and 85 of the battery assembly 81 and at the other end to the control board 12 as the voltage detecting terminals 96. Each of the bus bars 94 is bent and partially embedded in one of the first and second retainers 91 and 92.

The connector 93 is made up of an upper and a lower connecting bar 98. In other words, the connector 93 has a horizontal elongated opening or slit to have the upper and lower connecting bards 98. Each of the connecting bars 98 has a width which is, as can be seen from FIG. 12, small enough to be disposed in the space between the peripheral edges of the laminated films of vertically adjacent two of the cells 83. In the condition where the battery holder 82 is attached to the battery assembly 81, the connecting bars 98 each extend between the laminated films of the cells 83 without protruding from the periphery of the battery assembly 81. This is beneficial in reducing the overall size of the battery unit 10.

Each of the first and second retainers 91 and 92 has a height (i.e., a vertical dimension of the resinous body of each of the first and second retainers 91 and 92) which is, as can be seen in FIG. 2, smaller than an overall thickness of the battery assembly 81 (i.e., a vertical dimension of the battery assembly 81 in a direction in which the cells 93 are stacked). This enables the assembled battery module 11 to be mounted on the base 14 without physical interference of the retainers 91 and 92 with any parts of the battery unit 10.

FIG. 16 is a plane view which illustrates the assembled battery module 11 mounted on the base 14 to which the intermediate case 16 is attached.

As viewed from the connector 18 of the intermediate case 16, the assembled battery module 11 is placed with the electrode tabs 84 and 85 located on the right and left sides of the body of the assembled battery module 11. The assembled battery module 11 is also arranged adjacent the heat sink 27 on the base 14. The battery holder 28 is fit in one of the sides of the assembled battery module 11 which is closer to the heat sink 27, that is, the connector 18 and the connecting terminal 47. The assembled battery module 11 is fixed on the base 14 with mounting walls 97 of the battery holder 82 (i.e., the first and second retainers 91 and 92) being fastened to the fixing portions 24 c of the base 14 through screws N.

The double-sided tape (also called double stick tape) 111 is, as illustrated in FIG. 3, disposed below the body of the assembled battery module 11. The double-sided tape 111 bonds the bottom surface of the assembled battery module 11 to the base 14. The insulating sheets 112 are placed below the electrode tabs 84 and 85 of the battery assembly 81 to electrically isolate the electrode tabs 84 and 85 from the bottom plate 21.

Control Board 12

The structure of the control board 12 will be described below. FIG. 18 is a plane view which illustrates the control board 12 mounted on the base 14. In FIG. 18, a broken line indicates the location of the assembled battery module 11 for the sake of simplicity.

The control board 12 is made of a printed circuit board which has a variety of electronic devices mounted on a major surface thereof. The surface of the control board 12 on which the electronic devices are fabricated will also be referred to as an electronic component-mounted surface below. Specifically, the control board 12 is equipped with a CPU (i.e., an arithmetic device) working as controller to perform a given control task to control charging and discharging operations of the assembled battery module 11 and the above described power devices P. The control board 12 is laid to overlap with the assembled battery module 11 vertically, that is, arranged just above the assembled battery module 11 in the vertical direction thereof. In other words, the control board 12 is located farther away from the bottom plate 21 than the assembled battery module 11 is.

The control board 12 has the lower surface that is opposite the surface on which the power devices P, etc. are fabricated. The lower surface is placed on the fixing portions 24 a of the base 14 and fastened to the base 14 through the screws N. Specifically, the control board 12 is, as can be seen from FIGS. 3 and 18, fastened at a plurality of locations to the base 14 through the screws N.

The water detecting electrodes 68 of the water damage sensor 60 are located near the bottom plate 21 of the base 14 so that the CPU (i.e., the controller) on the control board 12 may analyze an output from the water damage sensor 60 which indicates the immersion of the battery unit 10 in water to perform given tasks to, for example, stop charging or discharging the assembled battery module 11 before the battery unit 10 breaks down due to the immersion thereof in water.

The control board 12 has two areas: an overlap area which is laid to overlap with the assembled battery module 11 vertically, that is, arranged just above the assembled battery module 11 in the vertical direction thereof and a non-overlap area which is located out of coincidence with the assembled battery module 11 in the vertical direction. The power devices P are fabricated on the non-overlap area. The non-overlap area is located just above, in other words, faces the heat sink 27 of the base 14, as illustrated in FIG. 5, thereby facilitating the release of heat, as generated by the power devices P, outside the assembled battery module 11 through the heat sink 27.

The insulating sheet 113 is, as illustrated in FIGS. 3 and 4, interposed between the board-facing plate 27 a of the heat sink 27 and the control board 12 to electrically isolate the heat sink 27 from the control board 12.

The joining of the control board 12 to the base 14 is achieved by inserting the terminal pins 53 and the connecting terminals 63 of the intermediate case 16 and the power terminals 95 and the voltage detecting terminals 96 of the assembled battery module 11 into holes formed in the control board 12 and then soldering them.

A temperature sensor 106 made of a thermistor is, as illustrated in FIG. 18, connected to the control board 12 through wires 105. The temperature sensor 106 is mounted on the assembled battery module 11 and works to measure the temperature of the assembled battery module 11. Specifically, the battery holder 82 of the assembled battery module 11 has, as illustrated in FIG. 12, a sensor mount 107 extending upward. The temperature sensor 106 is affixed to the sensor mount 107.

The battery unit 10 is, as described above, equipped with the pressing mechanism to press the assembled battery module 11 from above and hold it within the storage case 13. Specifically, the pressing mechanism is equipped with the coil springs 101, as illustrated in FIG. 2, arranged between the upper surface of the assembled battery module 11 and the cover 15 to press the assembled battery module 11 against the base 14. The installation of the coil springs 101 between the assembled battery module 11 and the cover 15 results in concern about physical interference between the control board 12 and the coil springs 101.

In order to alleviate the above problem, the control board 12 has a hole 102 passing through the thickness thereof to define a spring chamber in which the coil springs 101 are disposed. Each of the coil springs 101 has a length (i.e., an axis) which expands or contracts and is, as clearly illustrated in FIG. 2, disposed in the hole 102 with the length extending substantially perpendicular to the major surface of the control board 12. The hole 102 serves as an interference avoider to eliminate the physical interference between the control board 12 and the coil springs 101. The control board 12 is of a doughnut shape as a whole. The hole 101 is, as shown in FIGS. 17 and 18, of a polygonal shape, but may be circular.

Supplementing the explanation of the above pressing mechanism, the assembled battery module 11 has a central area of one of the opposed major surfaces thereof on which pressure, as produced by the coil springs 101, is exerted. In other words, the coil springs 101 are disposed on the central area of the upper surface of the assembled battery module 11. Such a central area will also be referred to as a pressure-exerted area below. The pressure-exerted area occupies the center of gravity of the assembled battery module 11 in a planar view thereof. The pressing mechanism has the four coil springs 11 arranged in a 2-by-2 matrix. The control board 12 is laid to overlap the center of gravity of the assembled battery module 11 in the vertical direction (i.e., the thickness-wise direction of the battery unit 10). Specifically, the hole 101 is formed in an area of the control circuit board 12 which covers or overlap the center of gravity of the assembled battery module 11 in the thickness-wise direction of the battery unit 10 (i.e., a direction in which the pressure, as produced by the coil springs 101, acts on the assembled battery module 11). In other words, the pressing mechanism (i.e., the coil springs 101) is so located as to exert mechanical pressure on the center of gravity of the assembled battery module 11 through the upper surface of the assembled battery module 11.

The rigid plate 87 is, as described above, affixed to the upper surface of the battery assembly 81 of the assembled battery module 11. The coil springs 101 are disposed on the rigid plate 87. The cover 15, as described already, has formed on the lower surface thereof the spring holder 35 which retains the ends of the coil springs 101. Specifically, the spring holder 35 has the chambers 35 a in which the coil springs 101 are put, respectively, so that the coil springs 101 are located in place on the pressure-exerted area of the assembled battery module 11.

The cover 15 is joined to the base 14 and compresses the lengths of the coil springs 101 to produce mechanical pressure. The mechanical pressure is exerted on the assembled battery module 11. Use of the four coil springs 101 results in an increase in area of the assembled battery module 11 (i.e., the pressure-exerted area) on which the mechanical pressure, as produced by the coil springs 101 acts. Use of the rigid plate 87 achieves uniform distribution of the mechanical pressure over the upper surface of the battery assembly 81 of the assembled battery module 11.

Electrical Structure of Vehicle Power Supply System

The electrical structure of the in-vehicle power supply system will be described below with reference to FIG. 19. The assembled battery module 11 of the battery unit 10 is, as described above, equipped with the four cells 83 connected in series. Each of the cells 83 is connected at the positive and negative terminals thereof to a controller 122 through electric paths 121. The controller 122 is implemented by a CPU (i.e., an arithmetic device) working to perform a given control task to control the charging or discharging operation of the assembled battery module 11. The controller 122 is an electronic part mounted on the control board 12. The bus bars 94 (94 a to 94 e), as illustrated in FIG. 13, are connected to the positive and negative terminals of the cells 83. The electric paths 121 are provided by the bus bars 94 and the voltage detecting terminals 96.

The battery unit 10 is equipped with connecting terminals 123 and 124 which are coupled together through a wire 125. The assembled battery module 11 is connected to a wire 126 diverging from the wire 125. A switch 127 is disposed in the wire 135. A switch 128 is disposed in the wire 126. Each of the switches 127 and 128 functions as a power control switching device made of, for example, a power MOSFET. The switches 127 and 128 correspond to the power devices P, as illustrated in FIG. 17. The sensor substrate 62 of the water damage sensor 60 is connected to the controller 122.

The power supply system includes a lead-acid storage battery 131 in addition to the battery unit 10. The lead-acid storage battery 131 is coupled to the connecting terminal 123 of the battery unit 10. The battery unit 10 and the lead-acid storage battery 131 are charged by an electric generator (also called an alternator) 132 installed in the vehicle. The vehicle is also equipped with a starter 133 as an electric load which is supplied from electric power from the lead-acid storage battery 131 to start an internal combustion engine mounted in the vehicle. To the battery unit 10, an electric load 134 such as an audio system or a navigation system mounted in the vehicle is coupled through the connecting terminal 134. The battery unit 10 supplies electric power to the electric load 134.

The on/off operation of the switch 127 controlled by the controller 122 will be described briefly. The switch 127 is opened or closed depending upon a state of charge (i.e., an available amount of electric energy) in the assembled battery module 11 and the lead-acid storage battery 131. Specifically, when the state of charge in the assembled battery module 11 is greater than or equal to a given value K1, the controller 122 turns off the switch 127 to disconnect the connecting terminal 123 and the assembled battery module 11. Alternatively, when the state of charge in the assembled battery module 11 has dropped below the given value K1, the controller 122 turn on the switch 127 to connect the connecting terminal 123 and the assembled battery module 11 to charge the assembled battery module 11 through the generator 132.

When it is required to start the engine using the starter 133, and the state of charge in the lead-acid storage battery 131 is greater than or equal to a given value K2, the controller 122 turns off the switch 127 to supply the electric power from the lead-acid storage battery 131 to the starter 133. Alternatively, when the state of charge in the lead-acid storage battery 131 is less than the given value K2, the controller 122 turns on the switch 127 to supply the electric power from the assembled battery module 11 to the starter 133.

The vehicle on which the power supply system is mounted is equipped with an automatic idle stop system (also called an automatic engine start/restart system) which works to automatically stop the engine when an ignition switch is in the on-state. When a given automatic engine stop condition is met, an ECU (i.e., an idle stop ECU) mounted in the vehicle stops the engine automatically. When a given automatic engine restart condition is met after the stop of the engine, the ECU restarts the engine using the starter 133. The automatic engine stop condition is, for example, a condition where an accelerator of the vehicle has been turned off or released, a brake of the vehicle has been turned on or applied, and the speed of the vehicle is less than a given value. The automatic engine restart condition is, for example, a condition where the accelerator has been turned on, and the brake has been turned off.

Installation of Battery Unit 10

The battery unit 10 is mounted on a floor of the vehicle which defines a passenger compartment. More specifically, the bottom plate 21 of the base 14 is disposed horizontally beneath front seats of the vehicle. The battery unit 10 is in the passenger compartment of the vehicle, so that there is a low possibility that the battery unit 10 is splashed with water or mud as compared with the case where the battery unit 10 is mounted inside an engine compartment of the vehicle. The battery unit 10 may alternatively be placed other than beneath the front seats, for example, in a space between rear seats and a rear luggage compartment.

The above described embodiment offers the following advantages.

When only the cover 15 is secured to the base 14 of the storage case 13, a square space (i.e., a clearance) is created between the cover 15 and the base 14, that is, in the peripheral wall of the storage case 13. The square space extends along the entire circumference of the peripheral wall of the storage case 13. The square intermediate case 16 is used to occupy the square space to form a portion (i.e., the intermediate wall 41) of the peripheral wall of the storage case 13. The use of the intermediate case 16 results in omission of a portion of the wall of either of the base 14 or the cover 15 which corresponds to the profile of the square space. The cover 15 is attached to the base 14, thereby ensuring a desired degree of mechanical strength of the base 14 and the cover 15 regardless of the intermediate case 16. Specifically, the intermediate case 16 is lower in stiffness than the base 14 and the cover 15, however, the attachment of the cover 15 to the base 14 ensures a required degree of mechanical strength of the storage case 13 independently of the intermediate case 16.

Consequently, when undesirable load arising from, for example, stepping on of the storage case 13, is exerted between the base 14 (i.e., the bottom of the storage case 13) and the cover 15 (i.e., the top of the storage case 13), a combination of the base 14 and the cover 15 bears the whole of the storage case 13 against the load to protect the battery unit 10 from the external force.

The attachment of the cover 15 to the base 14 permits the intermediate case 16, as described above, to be lower in stiffness than the base 14 and the cover 15, thus allowing the intermediate case 16 to be made of a lightweight material or designed to have a lightweight structure. In the above embodiment, the base 14 and the cover 15 are each made of metal such as aluminum, while the intermediate case 16 is made of synthetic resin. This results in a decreased overall weight of the storage case 13, thus permitting the battery unit 10 to be lightweight, yet have mechanical strength great enough to withstand possible external forces.

A clearance or interspace is created between the top end of the upright wall 22 of the base 14 and the lower end of the intermediate wall 41 of the intermediate case 16 (i.e., the bottom of the groove 43), so that the upright wall 22 is not in direct contact with the intermediate wall 41 in the vertical direction of the storage case 13, in other words, the upper end of the upright wall 22 is placed at a given interval away from the lower end of the intermediate case 16 in the thickness-wise direction of the battery unit 10. Similarly, a clearance of interspace exits between the top end of the intermediate wall 41 of the intermediate case 16 and the lower end (i.e., the bottom of the groove 32) of the cover 15, so that the intermediate wall 41 is not in direct contact with the cover 15 in the vertical direction of the storage case 13, in other words, the upper end of the intermediate case 16 is placed at a given interval away from the lower end of the cover 15 in the thickness-wise direction of the battery unit 10. Such layout blocks the direct transmission of external force, as exerted on the cover 15 from above, to the intermediate case 16, thereby physically protecting the intermediate case 16 which is low in stiffness.

The sealing members 75 and 76 are disposed in the clearances between the top end of the upright wall 22 of the base 14 and the lower end of the intermediate wall 41 of the intermediate case 16 and between the top end of the upright wall 22 of the base 14 and the bottom of the groove 32 of the cover 15, thereby establishing the air or liquid tightness of the storage case 13. This eliminates the risk of intrusion of liquid (e.g., a drink spilled in the passenger compartment of the vehicle) into the battery unit 10 and also minimizes the leakage of gas, as produced by the assembled battery module 11, outside the battery unit 10.

The intermediate case 16 is equipped with the insulating walls 71 which work to electrically isolate the base 14 from the assembled battery module 11, thus ensuring the proper operation of the assembled battery module 11.

The insulating walls 71 extend downward from the intermediate wall 41 of the intermediate case 16 toward the bottom plate 21 of the base 14 and are laid to overlap or face the inner surface of the upright wall 22 in the horizontal direction of the battery unit 10. The insulating walls 71 are located between the upright wall 22 and the electrode tabs 84 and 85, thereby avoiding the electrical conduction of the electrode tabs 84 and 85 to the upright wall 22.

The intermediate case 16, as described above, has disposed integrally thereon the connector 18 and the connecting terminal 47 which are used as electrical connectors to external electrical devices such as a lead-acid storage battery and an in-vehicle ECU. The attachment of the connector 18 and the connecting terminal 47 to the intermediate case 16 is achieved by using portions of the intermediate wall 41, thus facilitating the ease of installation thereof in the intermediate case 16.

Modifications of the above embodiment will be described below.

The intermediate case 16 is secured to the base 14, however, may be fixed to the cover 15.

The intermediate case 16 is made from synthetic resin, however, may be made of another type of material as long as it is lower in rigidity than the base 14 and the cover 15 and permits the intermediate case 16 to be lightweight. For instance, the intermediate case 16 may be made of an electrically conductive metallic material, like the base 14 and the cover 15. As an example, the intermediate case 16 is made from aluminum, like the base 14 and the cover 15, but shaped to be thinner in thickness than the base 14 and the cover 15. The intermediate case 16 is not required to have a mechanical strength to bear a vertical load of the storage case 13 and thus permitted to be reduced in weight.

In the case where the intermediate case 16 is made from metal, the insulating walls 71 are preferably designed to have an insulating film adhered thereto to exhibit electrical insulation. Alternatively, the intermediate case 16 may be designed to have a major body made from metal and the insulating walls 71 made of synthetic resin.

The base 14, the cover 15, and the intermediate case 16 are all made of synthetic resin. The intermediate case 16 is, however, shaped to be lower in rigidity and weight than the base 14 and the cover 15.

The insulating walls 71 of the intermediate case 16 are, as described above, disposed between the upright wall 22 of the base 14 and the assembled battery module 11, however, may alternatively or additionally be located between the bottom plate 21 of the base 14 and the assembled battery module 11.

The connecting terminal 47 which is joined electrically to the terminal block 17 and the connector 18 may alternatively be disposed in or attached to two of four sides of the intermediate case 16, respectively. For instance, the connecting terminal 47 and the connector 18 are installed in perpendicularly-extending or diametrically opposed two of four side surfaces of the intermediate wall 41.

The control board 12 is, as already described, mounted within the storage case 13, however, may be disposed outside the storage case 13.

The base 14 is, as clearly illustrated in FIG. 2, located vertically beneath the cover 15. The battery unit 10 is installed transversely. The base 14 and the cover 15 may alternatively be arranged adjacent each other horizontally, while the battery unit 10 is placed vertically.

The battery unit 10 is, as described above, mounted beneath the seats in the passenger compartment of the vehicle, however, may be disposed inside a dashboard or an engine compartment of the vehicle.

Each of the cells 83 is, as described above, implemented by a laminated-type cell, however, may be made of a can-type battery cell. Each of the cells 83, as used in the above embodiment, is a lithium-ion storage cell, but may be implemented by another type of secondary cell such as a nickel-cadmium storage cell or a nickel-hydrogen storage cell(s).

The battery unit 10 may be used with hybrid vehicles equipped with an internal combustion engine and an electric motor for driving road wheels or an electric vehicle equipped with only the electric motor as a drive source.

While the present invention has been disclosed in terms of the preferred embodiments in order to facilitate better understanding thereof, it should be appreciated that the invention can be embodied in various ways without departing from the principle of the invention. Therefore, the invention should be understood to include all possible embodiments and modifications to the shown embodiments which can be embodied without departing from the principle of the invention as set forth in the appended claims. 

What is claimed is:
 1. A battery unit comprising: a battery; a storage case in which the battery is installed, the storage case including a first casing member, a second casing member, and an intermediate casing member, the first casing member defining a bottom of the storage case, the second casing member defining a top of the storage case with the battery disposed between itself and the first casing member, the second casing member being joined to the first casing member so as to create a clearance which extends along a circumference of a peripheral wall of the storage case, the intermediate casing member being disposed between the first casing member and the second casing member to form an intermediate wall that is a portion of the peripheral wall of the storage case, the intermediate casing member being lower in stiffness than the first and second casing members; and a pressing mechanism comprised of at least one coil spring, the at least one coil spring being disposed between the second casing member and a major surface of the battery, the at least one coil spring provided so as to exert mechanical pressure on a center of gravity of the battery through the major surface of the battery, and thereby retaining the battery within the storage case, wherein the intermediate casing member is fixed on the first casing member, each of the second casing member and the intermediate casing member being equipped with a fixing portion which is secured to and in contact with the first casing member in the same direction as that in which the second casing member is joined to the first casing member, and wherein one of opposed ends of the intermediate wall that faces the first casing member is placed at a given interval away from one of opposed ends of the first casing member, and the other end of the intermediate wall is placed at a given interval away from one of opposed ends of the second casing member, and wherein the second casing member has ribs formed thereon to reinforce the second casing member against a reactive force arising from a mechanical pressure on the center of gravity of the battery.
 2. A battery unit as set forth in claim 1, wherein sealing members are disposed in the intervals between the intermediate casing member and the first casing member and between the intermediate casing member and the second casing member, respectively.
 3. A battery unit as set forth in claim 1, wherein the first casing member is made of an electrically conductive material, and wherein the intermediate casing member is equipped with an insulating wall disposed between the battery mounted on a bottom of the first casing member and the first casing member.
 4. A battery unit as set forth in claim 3, wherein the first casing member has the bottom on which the battery is mounted and an upright wall which extends from the bottom and encompasses the battery, wherein the intermediate wall of the intermediate casing member is located over the upright wall of the first casing member and continues to the upright wall, and wherein the insulating wall extends from the intermediate wall toward the bottom of the first casing member and is laid to overlap an inner surface of the upright wall and is interposed between the upright wall and electrodes of the battery.
 5. A battery unit as set forth in claim 1, wherein the intermediate casing member is equipped with connectors which establish electrical connections with an external electrical device.
 6. A battery unit as set forth in claim 1, wherein the ribs radially extend on a surface of the second casing member.
 7. A battery unit as set forth in claim 1, wherein the second casing member includes a spring holder that has a chamber in which the coil spring of the pressing mechanism is retained, and wherein the ribs extend radially from the spring holder.
 8. A battery unit as set forth in claim 1, wherein the second casing member includes a spring holder that has a chamber in which the at least one coil spring of the pressing mechanism is retained, and wherein at least some of the ribs extend radially from the spring holder, and at least some others of the ribs extend coaxially around the spring holder. 